DESCRIPTION: (Adapted from Applicant's Description) The investigators propose to examine further the roles of Prostaglandins (PGs) catalyzed by cyclooxygenases (COX-1 and COX-2) during various phases of uterine receptivity using mice mutated for the COX-1 or COX-2 gene. They also plan to examine whether leukotrienes (LTs) alone or with PGs play any roles in implantation. The specific aims are to examine: (1) the expression of COX-1 and COX-2, and levels of PGs in the periimplantation uteri of wild-type, heterozygous or homozygous mice mutated for the COX-2 and COX-1 genes, respectively, (2) the expression of PG receptors, and (3) of (COX) 5-lipoxygenase (5-LO) and levels of LTs in the periimplantation uteri of these mice, as well as (4) role of PGs/LTs in the attainment of uterine receptivity for implantation.